A potassium titanate is useful as a friction material for producing a friction sliding member e.g., brake lining, disc pad, and clutch facing) that is provided to a braking device used for automobiles, railroad vehicles, airplanes, industrial machines, and the like. A potassium titanate is represented by the general formula: K2O.nTiO2 (wherein n is an integer from 1 to 12). In particular; potassium hexatitanate represented by K2O.6TiO2 (n=6) has a tunnel crystal structure, and it is known that a friction material that includes fibrous potassium hexatitanate (fibrous potassium hexatitanate particles) exhibits excellent heat resistance and the like.
However, a fibrous potassium titanate is bulky, and exhibits inferior formability. Moreover, it is difficult to uniformly disperse a fibrous potassium titanate in a friction material due to low fluidity (i.e., a fibrous potassium titanate is difficult to handle).
In view of this problem, a non-fibrous potassium titanate obtained by grinding calcined potassium hexatitanate using an impact mill has been proposed (see Patent Literature 1 (JP-A-2008-110918)). Patent Literature 1 discloses a non-fibrous potassium titanate that includes a powder having a diameter of 3 μm or less, a length of 5 μm or more, and an aspect ratio (length/diameter ratio) of 3 or more (as measured using an electron microscope) in a ratio of 0.7 to 3.0%. However, a production method that can further reduce the content of a fibrous potassium titanate has been desired.
A method for producing potassium hexatitanate having a high single phase ratio has also been desired.